During Phase I, SEO will carry out experimental measurements of backscattered light for aerosol cloud of Bacillus globigii (BG), growth media, and kaolin particles. First parameter to be evaluated is the depolarization ratio. The theoretical calculations support the possibility of discrimination of bioparticles based on polarization properties. Second parameter to be evaluated is a circular dichroism (CD) of backscattered signal. Technically, circular polarized (left/right) laser light will be transmitted to carry out those measurements. Backscattered light will be detected, and the ratio of signal intensities for left- and right-circular polarized excitation will be recorded. Third, we will measure an off-axis contribution into backscattering signal by varying the opening of the diaphragm in front of the detector. Here, we first have to find out, whether a multiple scattering will be reasonably high for the realistic concentration of bioparticles. If so, we will carry out an experimental measurements for the clouds and build a multiple scattering model to characterize and discriminate the biological particles.The goal of Phase I is to get solid experimental data for aerosol cloud of biological/nonbiological particles, and make a conclusion - which of proposed techniques (depolarization, CD, and off-axis) works best. Based on the best choice, SEO will design characteristics and project performance of eye-safe man portable lidar to be build during Phase II. The successful development of polarization and/or multiple scattering techniques for the discrimination of biological agents will reduce the probability of false alarm.
Keywords: LIDAR, Depolarization, Circular Dichroism, Multiple Scattering, Optical Parametric Oscillator
